Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$224.92	13.737%	$255.8173	$255.82	$255.80	$255.80
Purchase #2	$32.27	8.402%	$34.9813	$34.98	$35.00	$35.00
Purchase #3	$215.72	10.327%	$237.9974	$238.00	$238.00	$238.00
Purchase #4	$169.72	12.712%	$191.2948	$191.29	$191.30	$191.30
Purchase #5	$202.89	13.467%	$230.2132	$230.21	$230.20	$230.20
Purchase #6	$72.89	11.629%	$81.3664	$81.37	$81.35	$81.40
Purchase #7	$58.79	4.583%	$61.4843	$61.48	$61.50	$61.50
7 purchase totals =	$977.20		$1,093.1547	$1,093.15	$1,093.15	$1,093.20